Refineries in the U.S. are processing increasingly heavy sour crudes that contain metals, sulfur, and high molecular weight aromatic hydrocarbons. Many sour crudes originate in the Western Hemisphere, including heavy crudes from Venezuela, Southern California, and the enormous quantities of oil sands in Canada. Processing and upgrading these heavy feedstocks requires considerable hydrogen. Since revamping or installing new hydrogen capacity with conventional technologies such as steam methane reforming, or petroleum coke gasification, are usually expensive, developing a process that can generate hydrogen from “bottom of the barrel” products presents an economically attractive alternative.
Currently, refiners make at least part of the hydrogen they use by steam-reforming methane or coke gasification. Naphtha is the heaviest feed that can economically be processed by conventional steam-reforming, and existing methods suffer from the limitation that heavy oils are not suitable as the feedstock.
Furthermore, hydrogen usage by petroleum refiners has been increasing. Approximately half of the petroleum refined in the United States is imported, and approximately half of that can be classified as heavy crude that contains high concentrations of sulfur, metals and high molecular weight hydrocarbons. Sulfur, metals and other contaminants are removed by hydrotreating, and high molecular weight hydrocarbons can be converted into lower molecular weight fractions by hydroprocessing. Very high molecular weight components such as asphaltenes are usually processed by coking. The reduction in allowable aromatic hydrocarbons and sulfur in gasoline and diesel, along with the need to process heavier crude oils, has increased the demand for hydrogen in the refinery.
The main commercial processes for the on-purpose production of hydrogen are steam reforming (natural gas or naphtha), partial oxidation (coal, coke, resid), or electrolysis of water. [Kirk-Othmer Encyclopedia of Chemical Technology, in Hydrogen by William F. Baade, Uday N. Parekh, Venkat S. Raman, Dec. 20, 2001, John Wiley & Sons.] Hydrogen is also commercially produced as a by-product of chemical processes (ethylene crackers, styrene, MTBE etc.) or gasoline manufacturing (catalytic reforming). Conventional steam reforming is a method for hydrogen production from hydrocarbon fuels such as natural gas. This is achieved in a processing device called a reformer which reacts steam at high temperature with the hydrocarbon fuel.
Scheme 1: Methane Steam ReformingCH4+2H2O→CO2+4H2 
Heavy oil (for example resid) and solids (coal) are used in oxidation or gasification processes to make hydrogen.
Scheme 2: Resid Partial Oxidation and Coal Gasificationresid partial oxidation: CH1.8+0.98H2O+0.51O2→CO2+1.88H2 coal gasification: CH0.8+0.6H2O+0.7O2→CO2+H2 
Selection of the differing processes is dependent on a number of criteria: (1) the availability and relative cost of the different feedstocks; (2) capital costs; (3) operating costs; (4) environmental considerations, and (5) end use of the hydrogen or syngas. Generally, as the feedstocks go from natural gas to light hydrocarbons to heavy hydrocarbons and then to solid feedstocks, the processing difficulty and capital costs increase. Partial oxidation (PDX) plants also require an air separation plant to produce the oxygen, larger water gas shift and CO2 removal facilities and gas cleanup systems due to impurities present in the solid feedstocks (such as sulfur) (Kirk-Othmer, 2001).
Heavier fractions, such as vacuum residue, deasphalter bottoms, refinery sludges, and petroleum coke, can be processed into hydrogen using PDX technology, however, the low hydrogen content of these feeds combined with a high capital and operating cost requires that they be available at very low or negative cost for a hydrogen only facility (Kirk-Othmer, 2001).
In the U.S., over 95% of on-purpose hydrogen production is supplied by steam methane reforming of light hydrocarbons. Many existing refinery and chemical hydrogen plants produce a medium-purity (95%-97%) hydrogen product by removing the carbon dioxide in an absorption system and methanating any remaining carbon oxides. Since the 1980s most SMRs use pressure swing adsorption (PSA) technology to recover and purify the hydrogen to purities above 99.9% (Kirk-Othmer, 2001).
When natural gas is used as the feed to a steam reformer, the basic reactions are (1) reforming and (2) shift.
Scheme 3: